1. Field of Invention
The present invention is generally related to wastewater treatment processes and equipment, and more particularly to use of microorganisms in the treatment of wastewater.
2. Description of Prior Art
In a typical arrangement, municipal wastewater is treated by using aerobic organisms to consume the toxic materials present in the wastewater (for this reason the wastewater is commonly referred to as xe2x80x9cfoodxe2x80x9d), or at least break the materials down into forms which may be safely discharged. This type of process results in quite effective treatment of the wastewater. However, the aerobic organisms require oxygen to survive and are therefore suspended in tanks which are continuously aerated. This aspect of an otherwise effective process contains its drawbacks.
The constant aeration required to maintain an adequate level of organisms requires a constant supply of energy, and the more organisms needed to ingest the toxic materials, the more energy is needed for aeration. Consequently, the energy costs associated with running this type of aerobic process can become quite high.
Quite often, the organisms will perpetuate in a highly oxidized environment, thereby resulting in a growth in the number of organisms. Assuming the food level (e.g. amount of influent introduced into the system) remains relatively level, this growth in organisms results in a low food to microorganism (xe2x80x9cF/Mxe2x80x9d) ratio. A low F/M ratio results in a condition known as xe2x80x9cbulking.xe2x80x9d Bulking is the point in the process where the organisms gain volume without increasing the processing of sludge.
When bulking occurs, a new breed of problems occur with the treatment process. For instance, the organisms begin to die and accumulate in the tanks. This build up results in odors being dissipated from the tank, and ultimately to the surrounding community. These organisms can also become airborne pathogens which are distributed in the treatment plant""s vicinity, thereby creating illness. Furthermore, the tanks have to be scrubbed quite often to prevent or at least minimize the attendant problems, thereby resulting in processing downtime and, creating more expense for the facility.
3. Objects and Advantages
It is therefore a principal object and advantage of the present invention to provide a process and apparatus for treating sludge in an economical fashion.
It is an additional object and advantage of the present invention to provide a process and apparatus for more efficiently processing wastewater.
It is a further object and advantage of the present invention to provide a process and apparatus that may be retrofit into conventional contact stabilization systems.
It is another object and advantage of the present invention to provide a process and apparatus that enhances phosphorous and nitrogen removal from the wastewater.
It is another object and advantage of the present invention to provide a process and apparatus that decreases sludge production relative to the state of the art.
It is yet another object and advantage of the present invention to provide a process and apparatus to provide a treatment plant with additional five-day biochemical oxygen demand without requiring additional process tankage.
Other objects and advantages of the present invention will in part be obvious, and in part appear hereinafter.
In accordance with the foregoing objects and advantages, the present invention provides an apparatus and associated process for treating municipal wastewater. The apparatus of the present invention generally comprises a wastewater contact tank that is broken into three distinct zones: a selector zone positioned between a stabilization zone and a contact zone. The entire influent is introduced into the selector zone which is maintained in an anoxic condition. Baffles positioned within the selector zone permit control of microorganisms levels present in the zone.
The wastewater introduced into the selector zone and treated via the microorganisms present therein, flows over a weir into the contact zone. In the contact zone, the solids suspended in the liquor (the mixture of the wastewater and activated sludge) settle to the bottom and pass through a line which returns it to the selector zone. The return line, however, includes a valve which controls the rate of passage. The treated wastewater (which includes waste activated sludge and treated water) passes from the contact zone into the clarifiers for final processing.
The waste activated sludge that settles to the bottom of the clarifier tanks returns via a line to the stabilization zone. This waste activated sludge provides a good source of bacteria. The waste activated sludge flows over a weir into the selector zone for further processing.
Both the contact zone and stabilization zone are maintained in an oxidized condition, thereby permitting the microorganisms present therein to survive. By maintaining the selector zone in an anoxic condition, however, the aerobic organisms need to find sustenance elsewhere. Accordingly, the organisms ingest the nitrogen and phosphorous present in the wastewater for sustenance, thereby enhancing the purity of the effluent ultimately discharged from the facility.
The present apparatus permits the F/M ratio of the system to be maintained at a high level at all times, thereby alleviating the bulking problem resulting from low F/M ratios. By balancing the level of mixed liquor suspended solids re-introduced into the selector zone via the valve on the return line with the rate of influent introduced into the selector zone, a high F/M ratio can always be maintained. The valve could be manually controlled or controlled via a microprocessor programmed with the influent rates.